For me, it was Conquest: Frontier Wars
A space-based RTS, utilizing a map of subsectors interconnected via wormholes. Resources could be harvested via buildings built in a ring around planets, or harvested from asteroids, gas fields, or the wrecks of lost ships
Each unit also has a supply capacity, so you have to maintain supply ships or fight in the vicinity of logistical buildings to keep up the fight
Races were pretty much starcraft: Terrans with big dreadnoughts and a few sneaky ships, Mantis as zerg with some heavy hitters but plenty of carriers, then Caelarians as robots with various tricksy options
It was a fun compstomp game, and my Austrian cousin burned me a disk, so I can only play with German audio. The OST is bombastic, but atmospheric for a space rts